The present disclosure relates to a coordinate measuring system, and in particular to coordinate measuring system having a laser line probe that acquires texture or color during the scanning process.
Portable articulated arm coordinate measuring machines (AACMMs) have found widespread use in the manufacturing or production of parts where there is a need to rapidly and accurately verify the dimensions of the part during various stages of the manufacturing or production (e.g., machining) of the part. Portable AACMMs represent a vast improvement over known stationary or fixed, cost-intensive and relatively difficult to use measurement installations, particularly in the amount of time it takes to perform dimensional measurements of relatively complex parts. Typically, a user of a portable AACMM simply guides a probe along the surface of the part or object to be measured. The measurement data are then recorded and provided to the user. In some cases, the data are provided to the user in visual form, for example, three-dimensional (3D) form on a computer screen. In other cases, the data are provided to the user in numeric form, for example when measuring the diameter of a hole, the text “Diameter=1.0034” is displayed on a computer screen.
To assist with measuring objects, one type of accessory that is commonly used on an AACMM is a laser line probe (LLP). An LLP is a triangulation-based, non-contact device that includes a projector and a camera. The projector includes a light source that emits a light, typically as a line. The projector also includes a lens that projects the emitted light onto an object. The emitted light may be laser light, partially coherent light, or incoherent light. The camera includes a camera-type imaging device, such as a charge-coupled device (“CCD”) or CMOS photosensitive array. The camera also includes a camera lens that captures the pattern of light on the object surface and projects it onto the photosensitive array. The camera is typically positioned adjacent the laser light source within the LLP device. The projector has a virtual emission point from which the line or stripe of light appears to “fan out” in an angle in one dimension and in a flat sheet in the orthogonal dimension. The camera has a camera perspective center through which rays of light from the pattern on the object appear to pass in traveling to the photosensitive array. The line segment between the virtual emission point and the camera perspective center is called the baseline, and the length of the baseline is called the baseline length.
The fan of light projected by the LLP strikes the surface of the object and forms a relatively bright stripe of light on the object surface. The camera captures the 3D silhouette or profile of the laser stripe projected onto the object. The LLP is moved by the user such that the projected line stripe extends over all or at least the desired portion of the object within the LLP's field of view. That way, by moving the LLP over the object, hundreds of cross sections of the object surface are captured as 3D point clouds of raw data. Some LLPs can capture 280 frames, or stripes, of 3D data per second, or approximately 560,000 points of data per second. Signal processing electronics (e.g., a computer or a processor) are provided that run software which processes the 3D raw point cloud data into the resulting 3D image of the object that includes dimensional measurements as obtained by the LLP and its laser stripe and triangulation measurement process.
The image of the reflected line on the imaging device normally changes as the distance between the imaging device and the object surface changes. By knowing the baseline distance, the orientation of the projector and camera with respect to baseline, and the coordinates on the photosensitive array of the imaged pattern of light, known triangulation methods may be used to measure 3D coordinates of points on the surface of the object. That is, as the LLP is moved, the imaging device creates an image of each projected line stripe. Any deviations on the photosensitive array from a straight line pattern may be translated into height variations on the object surface, thereby defining the object surface. In other words, the method described hereinabove digitizes the shape and position of the object within the field of view of the LLP.
In traditional LLP devices, the photosensitive array is generates a signal based on the brightness of the returned light. In other words, a gray-scale image of the surface may be acquired. Therefore, the color or texture of the surface is not acquired of the surface.
Accordingly, while existing laser line probes are suitable for their intended purposes there remains a need for improvements in acquiring color information of a surface being scanned with an LLP.